The present invention relates to a breath test for the diagnosis of Helicobacter pylori infection in the gastrointestinal tract and, more particularly, to a breath test which is rapid and convenient.
Gastrointestinal infections caused by Helicobacter pylori result in a variety of disorders, such as duodenal and gastric (stomach) ulcers [NIH Consensus Statement, 12:1-23, 1994]. Furthermore, these infections have been implicated in stomach cancer [The World Health Organization's World Health Report, 1996]. Clearly, rapid, accurate and non-invasive methods of detection of Helicobacter pylori are necessary.
A number of methods for such detection are currently available. For example, endoscopy of the stomach can be performed in order to obtain a tissue biopsy [Cutler, A. F. et al., Gastroenterology, 109:136-141, 1995]. The biopsy can then be examined by a number of methods, including microscopy and histological methods. Unfortunately, this procedure has a number of drawbacks. First, it is highly invasive. Second, the patient must be sedated during the procedure. Third, the test cannot measure Helicobacter pylori activity in "real time". That is, there is a significant delay between the time the Helicobacter pylori activity takes place, and the time such activity is measured by the test.
Another, somewhat less invasive test is a blood test. A sample of blood is withdrawn and tested for the presence of antibodies to Helicobacter pylori. This test also has a number of drawbacks. Like the biopsy test, the blood test cannot directly measure Helicobacter pylori activity, particularly since antibodies can remain in the body for 6-24 months after an infection has been eradicated. Thus, slick a test measures previous exposure to Helicobacter pylori and not necessarily a current infection. A far less invasive method is a breath test. As described in U.S. Pat. No. 4,830,010 to Marshall (hereinafter referred to as "Marshall"), this method involves orally administering isotopically-labelled urea to a subject and then analyzing exhaled breath of the subject for the presence of isotopically-labelled carbon dioxide or ammonia, which indicates the presence of an infection in the gastrointestinal tract. Helicobacter pylori produces a large quantity of the enzyme urease, which hydrolyzes urea to form carbon dioxide and ammonia. At least one isotopically-labelled product is then exhaled by the subject and can be detected in the exhaled breath of the subject by an appropriate measuring instrument. Thus, the breath test for diagnosing Helicobacter pylori is relatively non-invasive.
Unfortunately, this test is not sufficiently rapid to permit immediate measurement of Helicobacter pylori activity. For example, in the Marshall disclosure, the breath of the subject is collected twenty minutes after administration of the substrate, by bubbling through a scintillation solution. The solution is then placed in a scintillation counter, which is presumably not located at the physician's office. Thus, the subject must wait about twenty minutes to give the sample, and must then wait for the laboratory to return the results. Clearly, this method cannot be used to analyze and immediately give the results of the test, within the context of a single visit to the office of the physician, for example.
This basic urea breath test for the diagnosis of Helicobacter pylori infection in the gastrointestinal tract as been examined in the clinical literature. Again the results of the test cannot be provided immediately. For example, Koletzko and co-workers describe the analysis of such a urea breath test with an isotope-selective non-dispersive infrared spectrometer [Koletzko et al., Lancet, 345:961-2, 1995]. liven using such a sophisticated instrument, the subjects were still required to wait 15 and 30 minutes before breath samples were taken. Clearly, such a long delay to obtain breath samples, as well as the long wait between samples, is both inconvenient and potentially reduces patient compliance. The potential reduction in patient compliance can have serious consequences, since as noted above, Helicobacter pylori has been implicated in stomach cancer as well as ulcers.
Furthermore, the sample or samples are collected from the patient and then sent to a laboratory for analysis, causing a delay in the determination of the results and forcing the subject to return to the office of the physician in order to obtain the results. If the test does not yield meaningful results, the entire process must be repeated again. The requirement for multiple office visits also potentially reduces patient compliance.
The most rapid breath test currently proposed, the "Pytest" from Tri-Med Specialties, Charlottesvilee, N.C., USA, takes about 10-15 minutes to perform but uses carbon-14 isotopically-labelled urea, which is radioactive [Peura, D. A. et al., Am. J. Gastro., 91:233-238, 1996]. Thus, this test has all the disadvantages of radioactivity. Not only is radioactivity potentially hazardous, but it restricts the test to large testing centers which can handle such materials. Thus, the test could not be performed in the office of the average physician, so that multiple office visits are again required.
In both cases the patient must wait at least 10-15 minutes before the sample is collected partly because only one sample is taken. Thus, in order for the test to have sufficient sensitivity, the level of isotopically-labelled carbon dioxide must be relatively high. However, such a single point determination potentially decreases the accuracy of the test, as well as increasing the risk of ambiguous results.
A better breath test would involve the collection of multiple samples, yet would be sufficiently rapid to permit both the samples to be obtained and the results to be determined within a short period of time, for example about 15 minutes. Such a test should also be sufficiently simple for a physician, such as a gastroenterologist, to perform in the office, without the need for a special testing center or laboratory.
There is thus a widely recognized need for, and it would be highly advantageous to have, a breath test for the detection of Helicobacter pylori infection of the gastrointestinal tract in a subject, which is extremely rapid and which can provide results with relatively little delay, for example in the context of a single visit to a physician's office.